The present invention relates to an apparatus for controlling the pressurized air supply to an engine.
It is known that pressurized air is supplied to the intake passage of an engine in order to increase the power of the engine and to decrease fuel consumption. Thus, vehicle engines having superchargers to which this fact is applied have been widely used.
However, the operating conditions of the engine are continuously changing, and superchanging the engine is not necessarily preferred in all operating conditions. For example, when the engine is driven with a low load at a low speed or is idled, supercharging results in loss of power. Further, if the engine is driven with a high load at a low speed, supercharging results in knocking due to incomplete combustion.
In order to eliminate the drawbacks described above, a supercharger control valve is conventionally disposed at the upstream side of a throttle valve in the intake passage. Further, a supercharging passage is provided which by-passes the supercharging control valve, and an air pump acting as the supercharger is disposed in the supercharging passage. The supercharger control valve interlocks with the throttle valve through a link mechanism such that the supercharger control valve is opened when the throttle valve is closed, allowing supercharged air to escape to the upstream side of the intake passage.
However, the supercharged air need not always be supplied to the engine not only when the throttle valve is closed but also when the engine speed, the negative pressure of the intake manifold, engine temperature, or the like is low. Therefore, the conventional controlling means of a supercharger control valve which is interlocked with a throttle valve by way of a link mechanism cannot make highly precise supercharging control according to engine operating conditions.
Further, in the conventional controlling means, the throttle valve and the supercharger control valve cannot be controlled independently. Therefore, when the supercharger control valve remains closed due to accidental engagement of the link or valve mechanism thereby to hold the throttle valve in an open position, supercharging continues, and the engine speed increases uncontrollably.
Further, since the engine is driven with a low load at a low speed when the throttle valve is closed, another control apparatus is proposed. According to this apparatus, the opening of the throttle valve is detected. When the opening of the throttle valve is less than a predetermined value, a pressure difference between the upstream and downstream sides of the throttle valve in the intake passage moves the displaceable element of an actuator, such as a diaphragm whereby the supercharger control valve connected to the diaphragm is fully opened.
However, in the control apparatus using the actuator of this type, if the degree of the opening of the supercharger control valve is great, the stroke of the diaphragm must be large. As a result, a large actuator is required, durability of the diaphragm is degraded, and responsiveness of the diaphragm to the pressure difference is also lowered.